In a method of monitoring fluid usage in a fluid system, a proportional control valve is provided, including a valve element operable to control fluid flow from a fluid source to the fluid system. A first pressure upstream of the valve element and a second pressure downstream of the valve element are measured to identify a pressure differential across the valve element. In response to the identified pressure differential, the valve element is adjusted to one of a plurality of flow positions to adjust the pressure differential across the valve element to substantially match a predetermined pressure differential. A flow rate through the proportional control valve is determined based on the first pressure, the second pressure, and the adjusted flow position of the valve element. Based on the determined flow rate over time, an amount of fluid usage in the fluid system is determined.